Texas Astronomers Revive Idea For 'Ultimately Large Telescope' On the Moon (phys.org) 80
A group of astronomers from The University of Texas at Austin has revived an idea shelved by NASA to build a lunar liquid-mirror telescope on the moon to study the first stars in the universe. "The team, led by NASA Hubble Fellow Anna Schauer, will publish their results in an upcoming issue of The Astrophysical Journal," reports Phys.Org. From the report: These first stars formed about 13 billion years ago. They are unique, born out of a mix of hydrogen and helium gasses, and likely tens or 100 times larger than the Sun. New calculations by Schauer show that a previously proposed facility, a liquid mirror telescope that would operate from the surface of the Moon, could study these stars. Proposed in 2008 by a team led by Roger Angel of The University of Arizona, this facility was called the Lunar Liquid-Mirror Telescope (LLMT). NASA had done an analysis on this proposed facility a decade ago, but decided not to pursue the project. According to Niv Drory, a senior research scientist with UT Austin's McDonald Observatory, the supporting science on the earliest stars did not exist at that point. "This telescope is perfect for that problem," he said.
The proposed lunar liquid-mirror telescope, which Schauer has nicknamed the "Ultimately Large Telescope," would have a mirror 100 meters in diameter. It would operate autonomously from the lunar surface, receiving power from a solar power collection station on the Moon, and relaying data to satellite in lunar orbit. Rather than coated glass, the telescope's mirror would be made of liquid, as it's lighter, and thus cheaper, to transport to the Moon. The telescope's mirror would be a spinning vat of liquid, topped by a metallic -- and thus reflective -- liquid. (Previous liquid mirror telescopes have used mercury.) The vat would spin continuously, to keep the surface of the liquid in the correct paraboloid shape to work as a mirror. The telescope would be stationary, situated inside a crater at the Moon's north or south pole. To study the first stars, it would stare at the same patch of sky continuously, to collect as much light from them as possible. The team is proposing that the astronomical community revisit the shelved plan for a lunar liquid-mirror telescope, as a way to study these first stars in the universe.
The proposed lunar liquid-mirror telescope, which Schauer has nicknamed the "Ultimately Large Telescope," would have a mirror 100 meters in diameter. It would operate autonomously from the lunar surface, receiving power from a solar power collection station on the Moon, and relaying data to satellite in lunar orbit. Rather than coated glass, the telescope's mirror would be made of liquid, as it's lighter, and thus cheaper, to transport to the Moon. The telescope's mirror would be a spinning vat of liquid, topped by a metallic -- and thus reflective -- liquid. (Previous liquid mirror telescopes have used mercury.) The vat would spin continuously, to keep the surface of the liquid in the correct paraboloid shape to work as a mirror. The telescope would be stationary, situated inside a crater at the Moon's north or south pole. To study the first stars, it would stare at the same patch of sky continuously, to collect as much light from them as possible. The team is proposing that the astronomical community revisit the shelved plan for a lunar liquid-mirror telescope, as a way to study these first stars in the universe.
It won't work. (Score:4, Funny)
It won't work. Pretty soon there's going to be people stomping around all over the place, moon trucks driving past, far too many surface vibrations for a liquid mirror to be any use.
Re: (Score:3)
It can even work, but the cost will be, well... astronomical.
Re: It won't work. (Score:2)
Re: (Score:2)
nasa will need someone to tighten the various nuts and bolts.
when do we go
Re: (Score:3)
Not to mention the constant barrage of asteroids crashing into the moon due to a missing atmosphere is sure making some waves in the liquid mirror.
A quick look at the moon can already tell you that.
Re: (Score:3)
Not necessarily due to asteroids, but there are moonquakes. Not sure they'd be material to a telescope. There's also the constant threat of lunar dust, which tends to get electrostatically attacted to surfaces; I'm not sure what impact it would have on the mirror. Without seeing their paper, I have no clue how they plan to deal with this. The paper notes that another research paper raised this as an issue... and then cites no resolution:
Re: (Score:2)
Not to mention Darth Cheney's Moon Mirrors to banish darkness from the Earth.
They should try the asteroid belt.
Moon versus space (Score:2)
Why not build it in space? What does having it sitting on the moon buy us? Seems like it would be easier to construct the thing free floating in space. You can have solar panels or whatever power source on the back of it and it may be easier to steer.
Re:Moon versus space (Score:5, Informative)
Liquid mirrors don't work in zero gravity...
Building it on the Moon buys us physics that makes it so when you spin the liquid, it creates a paraboloid rather than spinning it and creating a 'donut' or 'tube' of the liquid.
Re: (Score:3, Informative)
"Liquid mirrors don't work in zero gravity." False.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Re: (Score:2)
Technically they do, but you have to create artificial "gravity" by spinning it.
Constant spinning doesn't make a useful telescope.
Re: (Score:2)
Technically they do, but you have to create artificial "gravity" by spinning it.
Constant spinning doesn't make a useful telescope.
Of course constant spinning doesn't make a useful telescope, that's why the the moon scope is:
The telescope's mirror would be a spinning vat of liquid, topped by a metallic -- and thus reflective -- liquid
Axis (Score:3)
Of course constant spinning doesn't make a useful telescope, that's why the the moon scope is:
The telescope's mirror would be a spinning vat of liquid, topped by a metallic -- and thus reflective -- liquid
Getting the paraboid shape require spinning it around it centre's axis (around itself). Thus the telescope it doesn't change it bearing, it's constantly point the same direction, the one in which its axis of rotation point (and which works best if it is perpendicular to the the gravity).
Compensating for gravity requires yet another rotation: rotating sideways around a point which is further away down the line of the first rotation's axis (so that you create a centrifugal pseudo-force that makes up for the
Re: (Score:2)
I do wonder though if you could do it without spinning by using magnetism. Now, pure mercury isn't magnetic, it's very slightly diamagnetic, so you wouldn't be able to attract it with a magnet. There are liquid metals that are magnetic though. I'm not sure how much you would have to compromise on reflectivity. But you could conceivably have an adjustable mirror sitting on a matrix of electomagnets.
On the other hand, while the trick of spinning a liquid metal to make a curved mirror is neat, is it really a u
Re: (Score:1)
Re: (Score:2)
I suspect that they'd probably use an ionic liquid rather than mercury. Much lighter weight. Very low vapour pressure, probably much lower than mercury. Actually, now come to think of it... exactly how fast would a thin film of mercury evaporate in a vaccuum? Pretty quickly I'd imagine...
Re: Moon versus space (Score:2)
Yes, I think the original proposed liquid was a room temperature ionic liquid. In addition to low vapor pressure, RTILs also have extremely low melting points, so it would stay liquid even in the dark (and cold).
Good question about the mercury, which as I recall has something like a 2 mTorr vapor pressure at room temperature. That's small but large enough the you will get evaporative losses long term. Maybe if they had a big vat the replenish it...
I wonder what the plan would be for star tracking. The moon
Re: (Score:2)
Your description only describes one of the designs in the GP's link, and yes, if the rotation rate is low enough and/or the targets bright enough, it can be fine even in that case. For example, fixed zenith telescopes on Earth face a constantly moving background due to Earth's rotation.
Re: (Score:2)
Liquid mirrors don't work in zero gravity...
And in gravity, they work only if the telescope were to be fixed to point at the zenith. How useful is a telescope that cannot be repositioned?
Re: Moon versus space (Score:1)
Re: (Score:2)
If I were putting a telescope on the Moon, I would go with the composite mirror approach. This has now been well tested on Earth.
Re: Moon versus space (Score:1)
Re: (Score:2)
Now that private enterprise is in space, It's not going to take nearly that long.
Re: (Score:2)
Liquid mirrors don't work in zero gravity...
LOL durr
Building it on the Moon buys us physics that makes it so when you spin the liquid, it creates a paraboloid rather than spinning it and creating a 'donut' or 'tube' of the liquid.
Well there you have it, build the camera part around a donut lens. What's the holdup, Homer, you didn't eat the mercury donut did you?
If you're worried about the lens being too expensive, don't build a space telescope. Building on the moon to reduce lens cost is no good, you spend more compensating for moonquakes than you save with a cheap lens.
Re: (Score:2)
NASA need a reason to go to the moon beyond putting tokens on it.
Re: (Score:2)
Colonization is a perfectly good reason, and was sufficient to justify settling pretty much every scrap of usable land on Earth. There are plenty of people like me who would volunteer for a one-way ticket in a heartbeat.
The budget for the movie 'The Martian' was over $100,000,000 and it made over $630,000,000. How much would a real-time 24x7 live coverage of humanity's first attempt at migrating into the larger universe bring in?
Re: (Score:2)
Re: (Score:2)
Colonists die, some faster than others. They know that when they go in. During the colonization of the Americas and the Pacific sometimes most or all of a colony died out or just disappaeared. My own ancestors braved bears, starvation, wolves, Mormon marauders, mosquitoes, and incredible winters to settle the wilds of northern Michigan, they survived (by burning their furniture for heat one winter), many of their neighbors didn't. We still talk about them a century and a half later.
Re: (Score:2)
Re: (Score:2)
There is a big difference between volunteering to be the first pioneers from our planet and volunteering to assist in mass slaughter. I don't find the two situations to be at all analogous.
Re: (Score:2)
Re: (Score:2)
Ultimately Large Telescope... (Score:4, Funny)
Moving parts inevitably require maintenance (Score:2)
That’s gonna be on hellaciously expensive service call the first time some moon grit finds its way in and binds up the gears.
Re: (Score:2)
Gears? I'm no astrophysicist but if I were building something like this I'd want to use maglev and induction to support and rotate it. Then you only have to keep rocks out of the gaps.
Mylar film (Score:3)
Re: (Score:2)
An *infinitely* taut film would be flat.
A surface with zero tautness in zero gravity (think water drops in space) are round.
In between infinitely taut and zero, you get shapes that are in between a flat line and a circle. Which is pretty much a parabola*. As it happens, a parabola is exactly what you want for a telescope mirror.
* The shape you'd get isn't exactly the parabola you'd want for a flat secondary. It is, however, close and consistent in a mathematically predictable way. So just make your second
Re: (Score:2)
Mylar has wrinkles.
Re: (Score:1)
Re: (Score:2)
You're describing a "segmented mirror", which are used by the largest telescopes. But segmented mirrors can't just be clicked into a frame. In order to get sufficient precision, the mirrors need to be mounted on individual actuators which reposition them in response to microscopic shifts. The primary advantage of a segmented mirror approach is that we have experience building them at a larger scale than liquid mirrors.... but when you take into account the extra framing and machinery required, it would be a
Re: (Score:1)
Re: (Score:2)
Although a lunar telescope of regular segmented design can be made lighter and larger on the Moon due to the lower gravity, it will not get you close to a 100 meter aperture. The largest segmented mirror telescopes on Earth have about a 10 meter aperture. The lunar gravity of 1/6 Earth will allow scaling, using the same designs, to 6X of 60 meters, but not more. The rotating mirror offer the possibility to scale to larger sizes. On the other hand, if you accept the same limitation as the rotating mirror (it
Re: (Score:1)
Re: (Score:2)
Let's not forget that segmented mirrors, with individual mirrors that are microscopic, are already being manufactured on an industrial scale. DLP TVs use MEMs mirrors with very precise control to reflect an RGB source to produce an image. So, clearly the technology exists to create precisely controllable segmented mirrors on a massive scale. The weight and framing requirements seem like they would be lower than a liquid metal mirror at least.
Re: (Score:2)
Let's take that one bit at a time.
The MEMS tech used for DLP is not capable of precisely controlling mirrors. The individual elements can only be turned to two orientations. (Pulse width modulation is used to vary the apparent light level.) The technology absolutely exists to precisely control segmented mirrors, but it has nothing to do with DLP.
Neither segmented mirrors nor liquid mirrors have ever been used to construct a telescope on the order of 100m. Not by a long shot. The largest segmented mirror tel
Re: (Score:2)
Good point on how aimable the mirrors on a DLP tv array actually are. I think it's still a decent proof of concept that we can build big arrays of MEMS devices. As far as the weight goes, would the thickness of the fluid need to vary with the overall size? What about the rotation speed of the dish? Other posters have discussed potential evaporation and contamination issues with the fluid which might require thicker fluid or a large reservoir, not to mention the question of how you prevent the dish from defo
Re: (Score:2)
would the thickness of the fluid need to vary with the overall size?
Not significantly. Perhaps a little, if it turned out it was harder to shape the dish as precisely at larger size.... but I doubt that would make a big difference to the mass.
What about the rotation speed of the dish?
Nope! That's a cool thing about the forces involved -- a 1 inch mirror spins at the same rotational speed as a 1 mile mirror. (Which makes sense, if you think about it, because if you look at the middle part of a paraboloid, it's a smaller paraboloid.) The hoop forces on the outside of the dish would be greater, but not problematically
Re:Mylar film (Score:4, Informative)
It doesn't work because a "hanging thing" like that gives you a hyperbolic cosine, not a parabola. You really want a perfect parabola for a telescope.
Re: Mylar film (Score:2)
Re: (Score:1)
Re: (Score:3)
There is no wind on the moon, but there is gravity, so a telescope could be made from a gossamer thin mylar type film that could simply hang in a circular frame - a big tamborine. I don't see why it needs to be a spinning liquid.
People have tried this, but there are two reasons why it doesn't work well: it's very difficult to get the Mylar in the required parabolic shape, and more importantly, the surface finish of a telescope mirror needs to be perfectly shaped with the error less than a wavelength.
Mylar is not smooth enough at the microscopic level and also not thermally stable (if you hit it with light, it deforms enough to ruin the image). It's why we make telescopes out of special ceramics nowadays instead of much lighter plas
Future-proof your naming, people (Score:3)
Ultimately Large Telescope
Okay no. Because then what do you call the 120 meter telescope you make *next* year? What do you call the 300 meter telescope on Charon? Seriously, it's the "modernism" problem all over again.
Re: (Score:2)
... which is not to say that I'm enamored with names like "The Very Massive Very Very Very Wide Aperture Very Very Low Frequency Array". But at least there's room to grow there.
Re: (Score:1)
Re: (Score:1)
Ultimately Large Telescope.
Ultimately Larger Telescope
Ultimately Largest Telescope
Ultimately Immense Telescope
Ultimately Huge Telescope
So next 4 are covered :-D
Re: (Score:2)
They did have a project proposal called OWL - the "Overwhelming Large Telescope". This concept was for a 100 meter segmented mirror, different estimates of cost have been offered but it is clear that it would be the most expensive scientific instrument ever built.
Re: (Score:1)
Re: (Score:2)
Ludicrously Large Telescope?
The Plaid Telescope.
Taxes and Moon Quakes (Score:1)
Why does everything have to be bigger in Texas? At least the scientific crowd in Texas is being true to the Texan nature of having to have the biggest Johnson of a telescope in human history. The idea if accepted will help make everyone else in the country send more taxes to Texas to keep them satisfied now that oil is in the tank. So I guess the idea will have some traction at least in Houston.
In theory the idea is great and could work but and this is a Texas sized big one would it survive moon quakes or
Re: (Score:2)
Why does everything have to be bigger in Texas?
Because it's always either too hot or too cold, and being larger means having a more favorable ratio of mass to surface area; both less insolation per unit of mass, and also less near-infrared radiation.
Or maybe it's because they're insecure about being surrounded by Mexico.
Re: (Score:2)
It could be because Alaska could cut itself in half and Texas would only be the third-largest state.
Re: (Score:2)
You'd have to pay me a frack of a lot more than that to live in Texas. If it gets colder you can always put on more clothes, but if it gets hotter you can only take so many off before the put you in the loony bin.
Bring production facilities there to build it (Score:2)
The facility for creating structures could be a metal refinery and a 3d printer, or a facility to create buildings out of moon rock, or a machine to dig caves.
Re: (Score:2)
Re: (Score:2)
Water is a bad choice, it freezes, boils and sublimates. It's mostly useful to maintain the biological organisms that will be needed to build and maintain the thing.
First things first (Score:2)
All for it (Score:2)
...if it gets the US to practicalize launch patterns, tech, and logistics to get a durable US base for any reason at the north or south pole of the moon, I'm all for it.
It's not going to happen, though.
The US populace, as much as we like our politicians to make happy noises about space exploration, has shown they ultimately don't give a crap about it, not in any meaningful way.
The wealthiest country ever in human history, we STILL can't afford all the crap we DEMAND from government. We borrow 20-25% of our
Re: (Score:2)
Truer words have never been spoken. I'd mod you up but I have no points today.
The cost will be... (Score:2)
... one astronomical unit.
Re: (Score:2)
But how many light years will it take to build?
Re: (Score:2)
We can only hope that it wont require too many light years.
I would expect that most years out there would be dark.
The worst telescope sales pitch of all time (Score:1)
it would stare at the same patch of sky continuously
This is the worst telescope sales pitch of all time.
Incidentally, can't you put many small telescopes in an array and simulate a much larger telescope? Why don't we put 100 Hubbles in orbit around the sun?
Re: (Score:2)
it would stare at the same patch of sky continuously
This is the worst telescope sales pitch of all time.
The idea is too look at that one patch really, really well. Drill down to small scale and dim images that cannot be seen in any other way.
Incidentally, can't you put many small telescopes in an array and simulate a much larger telescope? Why don't we put 100 Hubbles in orbit around the sun?
You can, if they are location relative to each other is known precisely to less than an optical wavelength. Segmented mirrors are sort of like that, the Large Binocular Telescope does exactly that.
To revive an idea (Score:2)
It must be dead as a door-nail for a reason.
What's wrong with the JWST? (Score:1)
A "liquid telescope" sounds like an intriguing project, yet it makes more sense to get the JWST in place first.
And, secondly, once deployed, we can see if any OOPSes! need fixing there! (Remember the HST mis-shaped mirror?!)